Electrophotography – Image formation – Fixing
Reexamination Certificate
2002-02-27
2003-12-23
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Fixing
C219S216000
Reexamination Certificate
active
06668151
ABSTRACT:
The present disclosure relates to the subject matter contained in Japanese Patent Application No.2001-230149 filed on Jul. 30, 2001 and Japanese Patent Application No.2001-366402 filed on November 30, which are incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic core, a magnetic field shield member, and an electrophotographic apparatus using them and in particular to a magnetic core suitably used for an inductance element such as a coil or a transformer with a magnetic substance installed to produce an electromagnetic characteristic, a magnetic field shield member, and an electrophotographic apparatus using them.
2. Description of the Related Art
A coil or a transformer of an inductance element is one of important parts of electronic machines and electric appliances as a part having inductance. In recent years, electronic machines such as mobile telephones, PHS, and portable computers have tended to be sophisticated, miniaturized, and manufactured at low costs, and high performance, miniaturization, and manufacturing at low costs have also been required for coils and transformers of parts used with the electronic machines.
Most of the size, performance, and cost of a coil or a transformer are determined by a magnetic core used with the coil or the transformer. If a material having large effective magnetic permeability is used as a magnetic core material, the self-inductance and mutual inductance of the coil or the transformer can be increased and parts can be miniaturized. In the coil or the transformer, the loss quantity as represented by the Q value of inductance is a parameter directly involved in the energy efficiency of the coil or the transformer, and the coil or the transformer having a large Q value, namely, a small loss quantity is assumed to be have good performance.
Hitherto, a silicon steel plate and a ferrite sintered compact have been used as magnetic core materials of coils and transformers. Since a metal material such as a silicon steel plate has large conductivity generally, if the metal material is localized in a changing magnetic flux, an eddy current occurs and heat is generated, namely, so-called eddy-current loss occurs. Thus, to use a metal material as a magnetic core, the magnetic core is formed as a structure of stacking several silicon steel plates each formed of thin metal material, thereby preventing the eddy-current loss.
With such silicon steel plate, the loss increases in a high-frequency band. Thus, in the high-frequency band, a ferrite sintered substance of a metal oxide material is used in place of the silicon steel plate.
However, the ferrite sintered substance has the disadvantages that it is not easy to work to any desired shape, that it is also poor in flexibility, and that it is at high cost. Then, use of a composite material comprising ferrite particles dispersed in resin has been proposed. The composite material can be provided as a material which is flexible and is also comparatively small in loss, but has small magnetic permeability and thus is not satisfactory as a magnetic core material.
As the magnetic core of a coil or a transformer, a plurality of portions, such as an E-shaped core and an I-shaped core, may be joined to form one magnetic core. In this case, if only a minute gap exists, it is comparable to the fact that magnetic circuit is largely cut. As the gap exists, the magnetic characteristic of the magnetic core is made worse and a magnetic field leakage occurs, causing an unnecessary electromagnetic field leakage to occur. A coil or a transformer is installed in various electric appliances; in recent years, when designing various electric appliances, it has become necessary to consider the effect of the magnetic flux leaked from such an electric appliance on a human body.
By the way, as image formation technology, electrophotography has become widespread because it provides many merits of high print speed, convenience of eliminating the need for providing a print plate each time, capability of providing images directly from various pieces of image information, comparatively small-sized apparatus, easiness to provide a full-color image, and the like.
An image formation apparatus (electrophotographic apparatus) adopting electrophotography generally forms an electrostatic latent image on the surface of a latent image receptor, brings charged toner into contact with the surface of the latent image receptor to selectively deposite the toner to form a toner image, and transfers the toner image to a record medium via or not via an intermediate transfer body and then fixes the toner on the surface of the record medium by heat and/or pressure, etc., thereby providing an image.
In such an electrophotographic apparatus, usually a fuser comprising a heating roll and a pressurizing roll abutting each other is used for fixing. A record medium on which an unfixed toner image is formed is inserted into a nip part formed by the heating roll and the pressurizing roll abutting each other, whereby the toner is fused by heat and pressure and is fixed on the record medium as a permanent image. A heating member, a pressurizing member shaped like an endless belt may be used in place of the heating roll and/or the pressurizing roll. The heating roll comprises a metal core containing a heat source such as a halogen lamp, the metal core being formed with an elastic layer and a release layer, and the heating roll surface is heated internally by the heat source.
In the fuser, it is desired to instantaneously heat the heating member of the heating roll, etc., and lessen the wait time (warm-up time) as much as possible from the viewpoint of energy saving and the viewpoint of preventing the user from waiting when using the image formation apparatus. However, with the fuser adopting a heating roll containing a heat source such as a halogen lamp, there is a limit to shortening the warm-up time for the reasons that it takes a considerable time in heating the halogen lamp itself, that it takes a time until heat propagates to the surface because heat is generated from the inside of the heating roll, that it takes a time in heating the whole because a heating roll core having a considerable heat capacity must be selected, and the like. If a halogen lamp is used as the heat source, so-called flicker phenomenon occurs in which an energization current flows transiently when the halogen lamp is turned on or off; this is also a problem.
In recent years, as a heating section used in the fuser, section using an electromagnetic induction heating technique has been studied in place of the heat source such as a halogen lamp (JP-A-2000-242108). In the technique, a magnetic field generated by a magnetic field generation section is made to act on a heating member having a conductive layer, whereby the heating member is heated by the electromagnetic induction action; the flicker problem is not involved and only the heated object can be heated instantaneously, so that the warm-up time can be shortened.
The electromagnetic induction heating technique can be applied to any of a roll-shaped member such as a heating roll or a pressurizing roll or a member shaped like an endless belt replacing either or both of the heating roll and the pressurizing roll as the heating member. With the roll-shaped member, only the vicinity of the surface contributing to fixing may be heated and the core need not be heated, so that energy saving can be accomplished. On the other hand, the member shaped like an endless belt is thin and thus has a small heat capacity and can accomplish energy saving of a still higher order.
The electrophotographic apparatus may adopt not only the technique of fixing a record medium to which an unfixed toner image is transferred from a latent image receptor or an intermediate transfer body by a separate fuser as described above (which will be hereinafter simply referred to as “transfer and fixing independent technique” in some cases), but also a transfer and fixing simultaneous t
Haseba Shigehiko
Oka Kanji
Uehara Yasuhiro
Fuji 'Xerox Co., Ltd.
Grainger Quana M.
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